1. Field
The present application is drawn to compositions and methods for the production, purification, formulation, and use of immunomodulatory eubacterial minicells for use in treatment of diseases, such as bladder cancer and other malignancies.
2. Description of the Related Art
The following description of the background of the invention is provided to aid in understanding the invention, but is not admitted to describe or constitute prior art to the invention. The contents of the articles, patents, and patent applications, and all other documents and electronically available information mentioned or cited in this application, are hereby incorporated by reference in their entirety to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. Applicants reserve the right to physically incorporate into this application any and all materials and information from any such articles, patents, patent applications, or other documents.
It is well known that the immune system plays an important role in the prevention of cancer. It is becoming increasingly clear that immune modulation may be an attractive therapeutic approach in the treatment of cancer. The longest standing marketed anticancer immunomodulatory therapy is a live attenuated strain of Mycobacterium bovis, Bacille Calmette-Guerin (BCG), which is used as a postoperative adjuvant therapy for the treatment of non-muscle invasive bladder cancer. Other non-marketed experimental anticancer immunomodulatory approaches include the use of other live attenuated species of bacteria such as Salmonella typhimurium, Bifidobacteria, Listeria monocytogenes, Streptococcus pyrogenes, Serratia marcescens, Clostridium novyi, Salmonella choleraesius, and Vibrio cholera. While somewhat effective, each strain used is limited by the risk of infection, fear of genetic reversion of live attenuated strains to pathogenicity, and sepsis. All of these approaches have been met with extreme toxicity reminiscent of the living bacterial infection with toxicity occurring at or near the most efficacious dose. This results in narrow therapeutic indices for each strain type.
To address toxicity issues with living bacteria as immunomodulatory therapy, others have attempted to use different bacterial components (as opposed to the whole living organism) to generate the same immunological effect. Experimental therapeutics of this type include purified bacterial toxins, purified pro-inflammatory lipopolysaccharides (LPS), purified teichoic acid (TCA), and other bacterial cell wall preparations and other bacterial sub-cellular fractions. These approaches have improved toxicity profiles but are with a concomitant loss of efficacy in some cases. Additionally, many only stimulate a polarizing immune response (either Th1 or Th2) with the majority stimulating Th2 (antibody generating) responses. It is reasonably well documented that a Th1 (cellular immune response) response seems to be preferential with respect to having an anti-tumor immunomodulatory effect. Last, these preparations can be difficult to manufacture at a scale and quality to support market demand and may only ultimately generate a subset of immune responses incapable of generating anti-tumor effects. In the case of protein toxins used in the treatment of most cancers, efficacy of the protein toxin is significantly limited by toxicity to normal tissues. In addition, drug pharmacokinetic (PK) parameters contributing to systemic exposure levels frequently are not and cannot be fully optimized to simultaneously maximize anti-tumor activity and minimize side-effects, particularly when the same cellular targets or mechanisms are responsible for anti-tumor activity and normal tissue toxicity. Again, this results in a very narrow therapeutic index, common for most protein toxins.
In addition to live bacterial vectors and bacterial components as immunomodulatory “generalists”, other investigators have attempted to develop different, specific Th1 immunomodulatory cytokines and chemokines as anticancer therapeutics. Examples include but are not limited to interferon gamma (IFN-γ), interferon alpha (IFN-α), granulocyte macrophage colony-stimulating factor (GMCSF), tumor necrosis factor alpha (TNF-α), interleukin-2 (IL-2), interleukin-12 (IL-12), and interleukin-18 (IL-18). Each of these approaches has been limited by unanticipated and severe toxicity with little or no immunological therapeutic benefit when administered alone. It is becoming somewhat clear that single cytokine or chemokine agents does not invoke the full spectrum of Th1 immune response needed to have an anticancer effect and that these factors are likely working in concert at varying levels that are dynamic over time. This is a nearly impossible cascade of immunological signaling events to recapitulate and orchestrate with a multiplex product formulation. Most single agent cytokines have failed clinically, the exception being pegylated interferon for the treatment of chronic hepatitis C viral infections.
Based on the observed limitations of these approaches to the development of immunomodulatory anticancer therapeutics, there is a need for an immunomodulatory therapy that could mimic a live bacterial infection without introducing the risk of infection and infection-associated toxicity while still invoking a potent and diverse enough immune response to impart anticancer activity.